Photosensitive compositions useful for forming active patterns, methods of forming such active patterns and organic memory devices incorporating such active patterns

ABSTRACT

Example embodiments herein relate to compositions useful in forming organic active patterns that may, in turn, be incorporated in organic memory devices. The compositions comprise N-containing conjugated electroconductive polymer(s), photoacid generator(s) and organic solvent(s) capable of dissolving suitable quantities of both the electroconductive polymer and the photoacid generator. Also disclosed are methods for patterning organic active layers formed using one or more of the compositions to produce organic active patterns, portions of which may be arranged between opposed electrodes to provide organic memory cells. The methods include directly exposing and developing the organic active layer to obtain fine patterns without the use of a separate masking pattern, for example, a photoresist pattern, thereby tending to simplify the fabrication process and reduce the associated costs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. nonprovisional application is a divisional under 35 U.S.C.§121 of U.S. application Ser. No. 11/655,171, filed Jan. 19, 2007, whichclaims priority under U.S.C. §119 to Korean Patent Application No.10-2006-0005828, which was filed on Jan. 19, 2006, and Korean PatentApplication No. 10-2007-0005362, which was filed on Jan. 17, 2007 in theKorean Patent Office, the entire disclosures of each of which are herebyincorporated by reference.

BACKGROUND

1. Field

Example embodiments include compositions useful in forming patterns fromactive layers during fabrication of memory devices, methods of formingactive patterns using such compositions, and organic semiconductordevices incorporating such active patterns. More particularly, exampleembodiments include compositions which are based on one or moreN-containing conjugated electroconductive polymers and at least onephotoacid generator that can be patterned without using a separatephotoresist pattern, methods of forming such patterns using suchcompositions, and organic memory devices comprising such an activepattern.

2. Description of the Related Art

With the recent impressive advances in the information and communicationindustry, demand for various types of solid state memory devices havebeen increasing. Particularly, portable terminals, versatile smartcards, electronic money, digital cameras, gaming devices, and MP3players require non-volatile memory devices, e.g., memory devicescapable of retaining data once the power is switched of Prevalent amongnon-volatile memories are flash memories that are based on siliconmaterials.

Conventional flash memories are restricted in the number of times thatthey can be erased and re-programmed, and tend to have relatively slowrecording rates. Further, the memory capacity of such devices inpredicated on large scale integration which requires the formation ofincreasingly fine structures, giving rise to increased production costsand/or complicated processing. Additionally, conventional flash memoriesare approaching limits beyond which further miniaturization of thedevice structures will reach physical and/or technical limitations.

As conventional flash memory devices reach these technical limitations,ongoing research and development efforts have been directed to theidentification, development and/or refinement of next-generationnon-volatile memories. These next-generation non-volatile memories areexpected to provide advantages over the conventional flash memorydevices including, for example, increased speed, reduced powerconsumption, increased capacity and/or reduced cost.

Depending on the material constituting the cell, next-generationmemories receiving particular attention include those that may beclassified as ferroelectric RAM, magnetic RAM, phase change RAM,nanotube memory, holographic memory and organic memory. Of thesedevices, the organic memory devices, which feature the use of an organicmaterial formed between two electrodes with a voltage applied thereto,operate on the principle of electrical bistability, a phenomenon inwhich a material exhibits two distinct states of conductivity at thesame applied voltage that can be utilized to form a memory cell. Thatis, the organic memory devices include memory cells that are capable ofsupporting the reading and writing of data values corresponding to a “0”and a “1” by altering the resistance of the organic material between thetwo electrodes in response to electrical signals of sufficient polarityand magnitude. As a result of these properties, organic memory devicesare expected to overcome certain of the problems associated withconventional flash memories and exhibit, for example, improvedprocessability, reduced production costs and/or increased degrees ofintegration while still maintaining the non-volatility memorycharacteristics.

An organic memory cell, as illustrated in FIG. 1, typically comprises alower electrode 10 and an upper electrode 30 with an organic activelayer 20 interposed therebetween. Typically, a memory device includes alarge array of such memory cells and certain peripheral circuitry forselectively addressing certain of the memory cells for writing data toand reading data from the accessed memory cells. In order to form suchmemory cell arrays, the organic active layer and the layers of electrodematerial need be patterned to define the individual memory cells.

Most conventional patterning methods employ heat or an e-beam fordepositing a shadow mask even when the active layer consists ofmonomers, or comprise selective exposure/etching steps utilizing aseparately formed photoresist pattern to form an active pattern. Forexample, a layer of an electroconductive material is formed across thesurface of a substrate to form a lower electrode. This layer ofelectroconductive material is then coated with a photoresist compositioncontaining an organic active material, portions of the photoresistcomposition are exposed to form an exposed photoresist layer. Theexposed photoresist layer is then developed to remove portions of thephotoresist layer, thereby forming a photoresist pattern that can, inturn, be used as an etch mask for removing exposed portions of theorganic active layer and the electroconductive layer to form an activepattern. These conventional photoresist techniques, however, arerelatively complicated and tend to increase the production costs due, inpart, to the use of expensive apparatus.

Conventional conjugated polymers are typically patterned using, forexample, soft lithography or ink jetting, but such techniques are notgenerally suited for production of highly integrated memory devices.Soft lithography takes advantage of a mechanism in which the activelayer is cured with heat or light, but the range of materials that canbe used in such a process is relatively limited. Ink jet technologies aswell tend to be generally suitable for less demanding device patternrequirements, by have proven generally unsuitable for forming patternshaving critical dimensions (CD) below a microns using currentlyavailable technology. Additional difficulties with conventional ink jettechnologies have been associated with the selection of proper solventsand the ability to control and maintain concentrations to a degreesufficient to maintain the desired feature sizing.

SUMMARY

Therefore, example embodiments are provided with respect to organicmaterials, methods of forming patterns from such materials and devicesincorporating such patterns are provided for addressing and improvingupon and/or overcoming certain of the problems associated withconventional materials, methods and devices. In particular, exampleembodiments are provided of materials and processes suitable for formingorganic active patterns without using separate photoresist patternsduring fabrication of such devices.

Example embodiments include compositions comprising: (a) an N-containingconjugated electroconductive polymer; (b) a photoacid generator; and (c)a solvent capable of dissolving both the electroconductive polymer andthe photoacid generator. Example embodiments of such electroconductivepolymers include, for example, aniline-based polymers and copolymers,pyrrole-based polymers and copolymers, and vinylpyridine-based polymersand copolymers. Example embodiments of the photoacid generators include,for example, onium salts and non-onium compounds.

Example embodiments include methods of forming organic active patternsduring fabrication of organic memory devices including a region of theorganic material interposed between a lower electrode and an upperelectrode, comprising: forming an active layer by applying a compositionincluding (a) an N-containing conjugated electroconductive polymer; (b)a photoacid generator; and (c) a solvent capable of dissolving both theelectroconductive polymer and the photoacid generator to a substrate andremoving a majority of the solvent; exposing selected regions of theactive layer by light exposure and then developing the exposed layer toobtain an organic active pattern. Example embodiments also includeorganic memory devices incorporating such an organic active pattern andmethods of fabricating such devices that utilize a composition and amethod according to example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the organic semiconductor materials, organicsemiconductor layers formed from such materials, organic semiconductordevices incorporating such organic semiconductor layers and theperformance of such organic semiconductor devices are addressed morefully below with reference to the attached drawings in which:

FIG. 1 is a schematic perspective view of a general memory cell array;

FIG. 2 is a schematic cross sectional view of an organic memory devicein accordance with an example embodiment;

FIG. 3A is a schematic view showing the process of fabricating anorganic memory device in accordance with an example embodiment;

FIG. 3B is a schematic view showing the process of fabricating anorganic memory device in accordance with another example embodiment;

FIGS. 4A and 4B are microphotographs of an organic active patternprepared using a composition according to Example 1 and a methodaccording to an example embodiment;

FIG. 5 is a graph in which the current of the organic memory devicefabricated according to Example 1 is plotted against voltage; and

FIG. 6 is a current-voltage (I-V) curve of a memory device fabricatedaccording to Example 1 embodiment with repeated cycling.

FIG. 7 is a current-voltage (I-V) curve of a memory device fabricatedaccording to an Example 2.

FIG. 8 is a microphotograph of an organic active pattern preparedaccording to an Example 2.

It should be noted that these Figures are intended to illustrate thegeneral characteristics of memory structures according to exampleembodiments in order to supplement the written description providedbelow. These drawings, however, are not necessarily to scale and may notprecisely reflect the characteristics of any particular embodiment, andshould not be interpreted as defining or limiting the range of values orproperties of embodiments within the scope of the disclosure. Inparticular, the relative positioning and sizing of atoms, bonds, layers,regions and/or device structures may be reduced, exaggerated orotherwise modified for clarity.

DETAILED DESCRIPTION

Example embodiments include compositions useful for formingelectroconductive patterns for organic memory devices, which comprise(a) a N-containing conjugated electroconductive polymer; (b) at leastone photoacid generator; and (c) at least one organic solvent or solventsystem capable of dissolving both the electroconductive polymer and thephotoacid generator.

In those portions of the composition exposed to UV beams, the photoacidgenerator generates acid that will interact with the electroconductivepolymer within the composition for forming patterns from the activelayer material. The electroconductive polymer in those portions of thecomposition coating exposed to UV light will undergo a change inchemical structure that will, in turn, modify the solubility of theexposed portions relative to the unexposed portions. This difference insolubility between exposed and unexposed regions of theelectroconductive polymer is utilized to form a pattern from the exposedlayer by removing the more soluble portions. For example, when thepolymer compound in the exposed portion is changed from a generallywater-insoluble form into a water-soluble form, as shown in Reactions IIand II, the water soluble region may then be removed by developing thepattern using water to leave a residual pattern of the generallywater-insoluble portions.

Example embodiments of compounds useful in formulating such compositionsincludes, for example, conjugated electroconductive polymers having oneor more amine groups. Such conjugated electroconductive polymers havingan amine group include, for example, aniline polymers and copolymers,pyrrole polymers and copolymers, and vinylpyridine polymers andcopolymers, and mixtures thereof. As used herein, the term polymerrefers to those polymeric compounds formed primarily from a singlemonomer while the term copolymer refers to those polymeric compoundsformed using at least two distinct monomers. Further as used herein, theterm “conjugated” encompasses both a first group of polymeric compoundscharacterized by alternating single and double bonds between adjacentcarbon atoms (and possibly nitrogen atoms in the case of heterogeneousring compounds) forming the polymer backbone including, for example,polymers formed using aniline, pyrrole or vinylpyridine monomers, aswell as a second group of polymeric compounds characterized both byalternating single and double bonds between adjacent carbon atoms (and,as noted above, possibly nitrogen atoms) and by amine groups arrangedbetween adjacent monomers, with the ring compound atoms and the nitrogenatoms of the amine groups cooperating to form the polymer backbone asillustrated, for example, in Formula V, infra. Indeed, without beingbound by theory, it is anticipated that many, if not all, conjugatedelectroconductive polymers having a number of amine groups correspondingto the size of the polymer will exhibit sufficient solubility and may,accordingly, used in formulating example embodiments of compositions.

Example embodiments of photoacid generators (PAG) suitable for use informulating example embodiments of the compositions include both oniumsalts, non-onium salts and may be used singly or in combinations andmixtures. The photoacid generator(s) content of the compositions maycomprise from 0.1 to 10 parts by weight based on 100 parts by weight ofthe total solid content, including the PAG(s), in the composition.Example embodiments of non-onium photoacid generators include, forexample, compounds corresponding to Formulas I to III.

wherein, R₆ and R₇ are independently selected from a group consisting ofC1-C10 straight and branched alkyl groups and C3-C10 cycloalkyl groups.

wherein, R₈ is selected from a group consisting of hydrogen, halogens,C1-C5 straight and branched alkyl groups, C1-C5 straight and branchedalkoxy and C1-C5 straight and branched haloalkyl groups; and R₉ isselected from a group consisting of C1-C10 branched and cyclic alkylgroups, C1-C10 alkylphenyl groups and C1-C10 haloalkyl groups.

wherein R₁₀ is selected from a group consisting of hydrogen, halogens,C1-C5 straight and branched alkyl groups and a trifluoromethyl group;and further wherein R₁₁ is selected from a group consisting of C1-C10straight, branched and cyclic alkyl groups, C1-C10 alkylphenyl groupsand C1-C10 haloalkyl groups, C7-C10 phenylalkyl groups, C1-C5 straightand branched alkoxy groups, a phenyl group and a tolyl group.

Example embodiments of photoacid generators corresponding to Formula Iinclude 1-cyclohexylsulfonyl-1-(1,1-dimethylethylsulfonyl)diasomethane,bis(cyclohexylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1-cyclohexylcarbonyl diazomethane,1-diazo-1-cyclohexylsulfonyl-3,3′-dimethylbutan-2-one,1-diazo-1-methylsulfonyl-4-phenylbutan-2-one,diazo-1-(1,1-dimethylethylsulfonyl)3,3-dimethyl-2-butanone, and1-acetyl-1-(1-methylethylsulfonyl)diazomethane. Example embodiments ofphotoacid generators corresponding to Formula II includebis(p-toluenesulfonyl)diazomethane,methylsulfonyl-p-toluenesulfonyldiazomethane,1-diazo-1-(p-toluenesulfonyl)-3,3′-dimethyl-2-butanone,bis(p-chlorobenzenesulfonyl)diazomethane, andcyclohexylsulfonyl-p-toluenesulfonyldiazomethane. Example embodiments ofphotoacid generators corresponding to Formula III include1-p-toluenesulfonyl-1-cyclohexyl carbonyl diazomethane,1-diazo-1-(p-toluenesulfonyl)-3,3-dimethylbutan-2-one,1-diazo-1-benzenesulfonyl-3,3-dimethylbutan-2-one, and1-diazo-1-(p-toluenesulfonyl)-3-methylbutan-2-one.

Example embodiments of onium salts useful as a photoacid generator inexample embodiments of the composition may be represented by Formula IV:

wherein, R₂₄ is selected from a group consisting of C1-C6 straight andbranched alkyl groups, a phenyl group and substituted and unsubstitutedphenylalkyl groups; R₂₅ is selected from a group consisting of hydrogen,halogens and C1-C4 straight, branched and cyclic alkyl groups; andfurther wherein X is selected from a group consisting of C1-C8 straight,branched and cyclic alkyl sulfonates and perfluoroalkyl sulfonates,naphthyl sulfonate, 10-camphor sulfonate, phenyl sulfonate, tolylsulfonate, dichlorophenyl sulfonate, trichlorophenyl sulfonate,trifluoromethylphenyl sulfonate, chlorine, bromine, SbF₆, BF₄, PF₆ andAsF₆.

Example embodiments of groups suitable for inclusion as X in Formula IVinclude, for example, triphenylsulfonium trifluoromethane sulfonate,triphenylsulfonium perfluorooctane sulfonate, triphenylsulfoniumperfluorobutane sulfonate, diphenyl-p-tolylsulfonium perfluorooctanesulfonate, tris(p-tolyl)sulfonium perfluorooctanesulfonate,tris(p-chlorobenzene)sulfonium trifluoromethane sulfonate,tris(p-tolyl)sulfonium trifluoromethane sulfonate, trimethylsulfoniumtrifluoromethane sulfonate, dimethylphenylsulfonium trifluoromethanesulfonate, dimethyltolylsulfonium trifluoromethane sulfonate,dimethyltolylsulfonium perfluorooctanesulfonate, triphenylsulfoniump-toluene sulfonate, triphenylsulfonium methane sulfonate,triphenylsulfonium butane sulfonate, triphenylsulfoniumn-octanesulfonate, triphenylsulfonium 1-naphthalene sulfonate,triphenylsulfonium 2-naphthalene sulfonate, triphenylsulfonium10-camphor sulfonate, triphenylsulfonium 2,5-dichlorobenzene sulfonate,diphenyltolylsulfonium 1,3,4-tri chlorobenzene sulfonate, dimethyltolylsulfonium p-toluenesulfonate, diphenyl tolyl sulfonium2,5-dichlorobenzene sulfonate, triphenylsulfonium tetrafluoroborate,triphenylsulfonium hexafluoroacetate, and triphenylsulfonium chloride.

The range of solvents suitable for use in example embodiments of thecomposition are not particularly limited, but will include thosesolvents capable of dissolving a sufficient quantities of both theheteroatom-containing conjugated electroconductive polymer(s) and thephotoacid generator(s) to obtain a composition having a satisfactorysolids content. It is expected that suitable solvents will include, forexample, ethyleneglycol monomethyl ether, ethyleneglycol monoethylether, methylcellosolve acetate, ethylcellosolve acetate,diethyleneglycol monomethyl ether, diethylene glycol monoethylether,propylene glycol methylether acetate, propylene glycol propyletheracetate, diethylene glycol dimethylether, ethyl lactate, toluene,xylene, methylethylketone, cyclohexanone, 2-heptanone, 3-heptanone,4-heptanone, and mixtures and combinations thereof.

In addition to a primary solvent or solvent mixture, example embodimentsof the composition may also include a co-solvent selected from a groupconsisting of N-methylformamide, N,N-dimethylformamide,N-methylacetamide, N,N-dimethyl acetamide, N-methylpyrrolidone,dimethylsulfoxide, alcohols, and mixtures and combinations thereof. Whenone or more co-solvents are incorporated, example embodiments of thecomposition may include 5 to 25 wt % of the conjugated electroconductivepolymer(s) and up to 10 wt % of the co-solvent(s) wherein the weightpercentages of the polymer(s) and co-solvent(s) are based on the weightof the primary solvent(s) included in the composition.

Depending on the intended application and processes, example embodimentsof the composition may also include one or more additives selected froma group including, for example, surfactants, stabilizers, coatmodifiers, dyes, viscosity modifiers as necessary to providecompositions having a desired combination of properties.

Example embodiments also encompass methods of forming organic activepatterns on, for example, organic memory devices using one or moreexample embodiments of the composition. Example embodiments of suchmethods include applying one or more example embodiments of thecompositions directly to a substrate to form a layer and exposingportions of the layer to energy, typically UV light, to form an exposedlayer. In the exposed portions of the layer, the photoacid generator(s)will be activated and react with the conjugated electroconductivepolymer(s) to alter the solubility of the polymer(s) relative to theunexposed portions of the layer. The exposed layer may then be developedthrough exposure to a suitable solvent for removing the more solubleportions of the layer, thereby forming a pattern comprising the residualportions of the layer. Because example embodiments of the methoddirectly expose and pattern the layer, there is no need for anadditional photosensitive layer, for example, photoresist, in order toform the desired pattern, thereby tending to reduce fabricationcomplexity and cost.

Example embodiments of methods for forming an organic active pattern foruse in an organic memory device typically include applying an exampleembodiment of the composition to a substrate surface and drying thecomposition to form a coating layer. Portions of this coating layer maythen be exposed to energy, for example, UV radiation, having anappropriate wavelength and energy sufficient to activate the photoacidgenerator(s) within the coating layer. Typically, the coating layer willbe exposed to UV light through a photomask on which a predeterminedpattern is provided for reproduction on the substrate. The substratessuitable for use in example embodiments of the invention are notparticularly limited and those skilled in the art will be able toidentify those substi ates that may be more suitable for particularapplications. Substrates may include, for example, insulators, forexample, glass and sapphire, semiconductors, for example, silicon andgermanium, surface-modified glass, and plastics, for example,polypropylene and activated acrylamide.

The composition may be applied to the substrate using any appropriateconventional technique, including, for example, spin-coating, inkjet-printing, roll-to-roll, spraying and/or thermal deposition (e.g.,using a low temperature organic evaporator) processes. Following thecoating process, most of the solvent remaining in the composition may beremoved using a soft-bake process to form the organic active layer. Thesoft-baking process may, for example, be conducted at a soft baketemperature from 80 to 110° C. for a bake period of from 1 to 10minutes. For many applications, it is expected that an organic activelayer formed by depositing the composition on the substrate surface to athickness of from about 50 to 3000 Å will provide acceptable results,but as will be appreciated by those skilled in the art, organic activelayers thicknesses below 50 or above 3000 Å may be more suitable in someapplications.

The exposure process will typically utilize a photomask on which apredetermined positive or negative pattern is provided positionedbetween a light source and the substrate whereby selected portions ofthe organic active layer can be exposed to light while adjacent portionsremain unexposed. As will be appreciated by those skilled in the art,the particular combination of wavelength(s), incident energy (W/cm²) andexposure time will vary depending on a number of factors well known tothose skilled in the photolithographic arts. The combination ofwavelength(s), energy and exposure time should, however, be sufficientto induce acid production by the photoacid generator(s) present in theorganic active layer. It is anticipated that in most instances a UVsource characterized by a wavelength from 150 to 400 nm, for example,365 nm may be used successfully for those combinations of exposure timeand energy intensity sufficient to provide adequate activation of thephotoacid generator which, in turn, increases the aqueous solubility ofadjacent polymers. In such instances, water may be used as thedeveloping agent to remove the exposed regions of the organic activelayer, thereby leaving a residual organic active pattern.

Example embodiments also encompass organic memory devices which comprisean organic active pattern fabricated from an example embodiment of anorganic active layer that extends between two electrodes. An exampleembodiment of such an organic memory device is illustrated in FIG. 2 andcomprises a substrate 210 on which a lower electrode 220 and an upperelectrode 250 are formed, with an organic active layer 240 arrangedbetween the two electrodes. An optional barrier layer 230 may beprovided on the lower electrode 220. Example embodiments of the organicactive layer 240 may typically exhibit a thickness from about 50 to 3000Å, but as will be appreciated by those skilled in the art, organicactive layers thicknesses below 50 or above 3000 Å may be more suitablein some applications.

Example embodiments of the compounds utilized in forming the organicactive layer 240 are selected for their ability to exhibit bistabilityin resistance performance that may, in turn, be utilized in impartingmemory properties to the device. Like conventional memory devices,example embodiments of the organic memory devices can be selectivelyforced into two distinct states, a conductive state (low impedancestate) and a non-conductive state (high impedance state). By controllingthe transition between the conductive state and the non-conductivestate, example embodiments of memory cells may be converted into one ormore additional intermediate states. The availability of one or moreintermediate states permits the fabrication of organic memory deviceshaving increased memory capacity. Unlike conventional memory deviceswhich provide only two states, organic memory devices exhibiting threeor more conduction states (e.g., high, mid, and low impedance states),additional information can be stored as multiple bits in a single memorycell.

The upper electrode 250 and the lower electrode 220 independentlycomprise an electroconductive material selected from a group consistingof metals, metallic alloys, metal nitrides, metal silicides, metaloxides, metal sulfides, carbon, electroconductive polymers, organicconductors, and combinations thereof. Example embodiments of theelectrode materials include, for example, aluminum (Al), gold (Au),silver (Ag), platinum (Pt), copper (Cu), titanium (Ti), tungsten (W),and indium tin oxide (ITO). In those instances in which the electrodescomprise only organic materials, the resulting memory device may consistonly of organic materials. As will be appreciated by those skilled inthe art, depending on the electrode materials utilized, a variety ofconventional formation processes, for example, deposition (e.g., thermaldeposition), sputtering, e-beam evaporation and spin coating, may beemployed.

Example embodiments of electroconductive polymers that are expected tobe useful in forming organic active patterns include, for example,polyphenylacetylenes, such as polydiphenyl acetylene,poly(t-butyl)diphenylacetylene, poly(trifluoromethyl)diphenyl acetylene,poly(bistrifluoromethyl)acetylene, polybis(t-butyldiphenyl)acetylene,poly(trimethylsilyl)diphenyl acetylene, poly(carbazol)diphenylacetylene,polydiacetylene, polyphenylacetylene, polypyridine acetylene,polymethoxyphenyl acetylene, polymethylphenyl acetylene,poly(t-butyl)phenyl acetylene, polynitrophenyl acetylene,poly(trifluoromethyl)phenyl acetylene, poly(trimethylsilyl)phenylacetylene, derivatives thereof, and polythiophenes.

Example embodiments of a memory device may, as illustrated in FIG. 2,include an optional barrier layer 230 formed on the lower electrode 220in order to reduce the likelihood of damage to the lower electrodeduring subsequent processing. Example embodiments of barrier materialsfor forming the barrier layer 230 include, for example, SiO_(x),AlO_(x), NbO_(x), TiO_(x), CrO_(x), VO_(x), TaO_(x), CuO_(x), MgO_(x),WO_(x) and AlNO_(x), with SiO₂, Al₂O₃, Cu₂O, TiO₂, and V₂O₃ expected tobe useful in a range of applications. Alternatively, the barrier layermay be made from one or more organic materials including, for example,Alq3 (aluminum tris(8-hydroxyquinoline), PMMA (polymethylmethacrylate),PS (polystyrene) and PET (polyethylene terephthalate). As will beappreciated by those skilled in the art, although the target thicknessof the barrier layer will be a function of various parameters including,for example, the barrier material(s) utilized, the electrode topographyand the subsequent processing, it is expected that a barrier layerthickness of 20 to 300 Å will be suitable for many applications.

By utilizing the change in electrical resistance of the organic activepattern for storing information in a memory cell, example embodiments ofthe memory devices will be non-volatile and may, therefore, be ofparticular usefulness in applications including, for example, mobileterminals, smart cards, electronic money, digital cameras, gamingdevices, MP3 players and other electronic devices that are usedintermittently and/or for which reduced power consumption isparticularly advantageous.

An example embodiment of a process for fabricating an organic memorydevice is illustrated in FIG. 3A in which a lower electrode 220 isformed on a substrate 210 and a barrier layer 230 is formed on the lowerelectrode. A composition comprising a mixture of electroconductivepolymer(s), photoacid generator(s) and solvent(s) is then applied to thebarrier layer and dried to form an organic active layer 240′. Afterbeing aligned under an appropriate photomask 300, predetermined regionsof the organic active layer 240′ are exposed to UV light. The exposedorganic active layer 240′ is then developed using an appropriate solventto remove the exposed regions of the exposed organic active layer, theremaining portions of the organic active layer comprising an organicactive pattern 240. An upper electrode 250 is then formed on the organicactive pattern, thereby providing organic memory cells comprising aregion of the organic active material arranged between the lower andupper electrodes for use in, for example, organic memory devices.

Another example embodiment of a process for fabricating an organicmemory device is illustrated in FIG. 3B in which a lower electrode 220is formed on a substrate 210 and a barrier layer 230 is formed on thelower electrode. A composition comprising a mixture of electroconductivepolymer(s), photoacid generator(s) and solvent(s) is then applied to thebarrier layer and dried to form an organic active layer 240′. Afterbeing aligned under an appropriate photomask 300, predetermined regionsof the organic active layer 240′ are exposed to UV light. The exposedorganic active layer 240′ is then developed using an appropriate solventto remove the non-exposed regions of the exposed organic active layer,the remaining portions of the organic active layer comprising an organicactive pattern 240. An upper electrode 250 is then formed on the organicactive pattern, thereby providing organic memory cells comprising aregion of the organic active material arranged between the lower andupper electrodes for use in, for example, organic memory devices.

A more thorough understanding of example embodiments may be realizedwith the following example, which is set forth to illustrate anembodiment of an electroconductive polymer, a photoacid generator and asolvent composition useful for forming organic active layers and anembodiment of a method for forming such a layer and forming an organicactive pattern for use in an organic memory device. This followingExample, therefore, should not be construed to limit unduly the exampleembodiments within the scope of the disclosure.

Example 1

A raw composition comprising (a) an electroconductive polymercorresponding to Formula V (illustrated below) and having a weightaverage molecular weight of about 50,000, (b) a photoacid generatorcorresponding to Formula VI (illustrated below) (wherein m=1 and n=1)and (c) a DMF (N,N-dimethylformamide) solvent was prepared by mixing theingredients to form a solution. The solution was then filtered through a0.2 μm Teflon filter to obtain a sample organic active composition.

A copper layer was formed on a silicon substrate for use as a lowerelectrode. A 20 nm barrier layer of LiF was formed on the copper layerusing a spin coating process to form a composite conductive layer on thesubstrate. The composite conductive layer was patterned and etched toform a lower electrode pattern. A volume of the sample organic activecomposition was then applied to the lower electrode pattern using a spincoating process to form an initial organic active layer which was thensubjected to a soft bake at 120° C. for 20 minutes to remove themajority of the solvent and obtain an organic active layer.

The coated substrate was then immersed for 1 minute in a 1 wt % solutionof HAuCl₄ in ethanol and then washed several times with deionized water.After the washing was completed, the coated substrate was immersed in a1 wt % solution of NaBH₄ in methanol for about 15 seconds and thensubjected to a second washing with deionized water. The coated substratewas then dried overnight at 60° C. under a vacuum.

A photomask was prepared by patterning and etching a chrome layer thathad been applied to a quartz plate to form a chrome pattern. Thephotomask was aligned with the coated substrate so that the chromepattern was adjacent the organic active layer. The organic active layerwas then exposed through the photomask using UV light having awavelength of 365 nm to form an exposed organic active layer. Theexposed organic active layer was then developed by exposing the activelayer to water for 30 seconds in water to form an initial pattern thatwas then washed with water for an additional 60 seconds to remove theexposed region of the organic film to obtain an organic active pattern.

An aluminum layer was then formed over the organic active pattern bydeposited aluminum using a thermal evaporation process and thenpatterned and etched to form an upper electrode. The organic activelayer and each of the electrodes were found to range in thickness from15 to 100 nm and from 50 to 100 nm, respectively, as measured with anAlpha-Step™ profilometer.

The microphotographs reproduced in FIGS. 4A and 4B illustrate theorganic active pattern obtained using the compositions and method asdetailed in the Example with FIG. 4B (right image) providing a magnifiedview of the area B indicated on FIG. 4A (left image) in which theorganic active pattern 240 and surface regions of the barrier layer 230′may be observed. As reflected in FIG. 4B, the organic active pattern 240was produced with widths as fine as 50 μm between adjacent activeregions without employing an expensive, complicated process such as anadditional photoresist process.

FIG. 5 illustrates a current-voltage (I-V) plot obtained using anorganic memory device fabricated in the manner detailed in the aboveExample. The voltage scan was conducted with 0.1 volts/sweep. As may beseen in FIG. 5, the current sharply increased near −4 V for the firstbias sweep, indicating the formation of a set state within the organicactive material, and drastically decreased at near −2.5 V, indicatingthe formation of a reset state. As may be seen in FIG. 5, the currentdiffered by as large as five orders of magnitude between the set stateand the reset state of the organic active material.

After the voltage was removed from the device in the set state, a secondsweep allowed the device to be in a high current state even at a lowvoltage. The organic memory device of example embodiments exhibitedelectrical bistability, i.e., it is capable of exhibiting two distinctresistivity states at the same applied voltage. Because these two statesof different resistivity may be read using a relatively low readingvoltage, devices incorporating such structures and materials may beuseful as memory devices. The bistability reflected in the data plottedin FIG. 5 generally indicates the utility of example embodiments ofmemory devices incorporating such organic active materials.

FIG. 6 is another current-voltage curve (I-V curve) generated from anorganic memory device fabricated according to the above Example. Thevoltage scan illustrated in FIG. 6 was conducted with 0.1 volts/sweepwith solid lines and dotted lines representing the measured currents andvoltages, respectively. As reflected in the data plotted in FIG. 6,example embodiments of organic memory devices are capable of switchingbetween the two resistivity states in a consistent and reproduciblemanner.

Although certain example embodiments have been disclosed forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions to the compositionsand methods are possible. Accordingly, insubstantial modifications,additions and substitutions should be understood as falling within thescope and spirit of the disclosure consistent with the exampleembodiments. For example, the compositions used forming patterns and themethod of forming patterns in accordance with example embodiments arenot limited to memory devices but may be applied to a range organicdevices including, for example, LEDs, photoelectric conversion devicesand display devices. In particular, organic memory devices incorporatingone or more electroconductive polymers incorporating an amine group areexpected to be useful for patterning metal filament memory devices.

Example 2

A raw composition comprising (a) an electroconductive polymercorresponding to the above Chemical Formula (weight average molecularweight of about 50,000), (b) a photoacid generator corresponding to ofthe following Chemical Formula VI (wherein m=1 and: n=1) and a DMFsolvent was prepared by mixing the ingredients to form a solution. Thesolution was then filtered through a 0.2 μm Teflon filter to obtain asample organic active composition.

An aluminum layer was formed on a silicon substrate for use as a lowerelectrode. A 20 nm barrier layer of LiF was formed on the copper layerusing a spin coating process to form a composite conductive layer on thesubstrate. The composite conductive layer was patterned and etched toform a lower electrode pattern. A volume of the sample organic activecomposition was then applied to the lower electrode pattern using a spincoating process to form an initial organic active layer which was thensubjected to a soft bake at 120° C. for 20 minutes to remove themajority of the solvent and obtain an organic active layer.

The coated substrate was then immersed for 1 minute in a 1 wt % solutionof HAuCl₄ in ethanol and then washed several times with deionized water.After the washing was completed, the coated substrate was immersed in a1 wt % solution of NaBH₄ in methanol for about 15 seconds and thensubjected to a second washing with deionized water. The coated substratewas then dried overnight at 60° C. under a vacuum.

A photomask was prepared by patterning and etching a chrome layer thathad been applied to a quartz plate to form a chrome pattern. Thephotomask was aligned with the coated substrate so that the chromepattern was adjacent the organic active layer. The organic active layerwas then exposed through the photomask using UV light having awavelength of 365 nm to form an exposed organic active layer.

The exposed organic active layer was then developed by exposing theactive layer to water for 30 seconds in water to form an initial patternthat was then washed with water for an additional 60 seconds to removethe non-exposed region of the organic film to obtain an organic activepattern.

A copper layer was then formed over the organic active pattern bydeposited aluminum using a thermal evaporation process and thenpatterned and etched to form an upper electrode. The organic activelayer and each of the electrodes were found to range in thickness from15 to 100 nm and from 50 to 100 nm, respectively, as measured with aquartz-crystal monitor.

FIG. 7 is a current-voltage curve (I-V curve) generated from an organicmemory device fabricated according to the above Example II. The voltagescan illustrated in FIG. 7 was conducted with 0.1 volts/sweep with solidlines and dotted lines representing the measured I-V (voltages andcurrents) and V-R (voltages and resistances), respectively. As reflectedin the data plotted in FIG. 7, example'embodiments of organic memorydevices are capable of switching between the two resistivity states in aconsistent and reproducible manner. The microphotograph reproduced inFIG. 8 illustrates the organic active pattern obtained using thecompositions and method as detailed in the Example 2. As detailed above,example embodiments of methods tend to reduce process complexity andcost by allowing fine patterns to be formed from an organic activematerial without using a conventional photoresist, thereby reducing orremoving the need for expensive apparatus and materials. Accordingly,example embodiments of organic memory devices utilizing such materialsand methods tend to reduce the fabrication cost, improve the processyield and/or improve the device yield.

1. A method of forming a memory cell comprising: forming a lowerelectrode pattern on a substrate; depositing a photosensitivecomposition on the lower electrode pattern to form a photosensitiveorganic active film, wherein the photosensitive composition includes aN-containing conjugated electroconductive polymer, a photoacidgenerator, and a solvent capable of dissolving both theelectroconductive polymer and the photoacid generator; exposing portionsof the organic active film to light of sufficient energy and wavelengthto activate the photoacid generator; developing the organic active filmusing a developer solution to obtain an organic active pattern; andforming an upper electrode pattern on the organic active pattern wherebyregions of the organic active pattern are arranged between correspondingportions of the lower electrode pattern and the upper electrode pattern.2. The method of forming a memory cell according to claim 1, wherein thedeveloping includes removing exposed regions of the organic active filmto obtain an organic active pattern.
 3. The method of forming a memorycell according to claim 1, wherein the developing includes removingnon-exposed regions of the organic active film to obtain an organicactive pattern.
 4. The method of forming a memory cell according toclaim 1, wherein the substrate is made from a material selected from agroup consisting of insulators, glass, sapphire, semiconductors,silicon, surface-modified glass, plastics, polypropylene, activatedacrylamide, and combinations thereof.
 5. The method of forming a memorycell according to claim 1, wherein the depositing includes a processselected from a group consisting of spin-coating and thermal deposition.6. The method of forming a memory cell according to claim 1, wherein theexposing portions of the organic active film utilizes lightcharacterized by a wavelength from 150 nm to 400 nm.
 7. The method offorming a memory cell according to claim 1, wherein the developersolution is an aqueous composition.
 8. A method of forming an organicmemory device comprising: forming a lower electrode pattern on asubstrate; depositing a photosensitive composition on the lowerelectrode pattern to form a photosensitive organic active film, whereinthe photosensitive composition includes a N-containing conjugatedelectroconductive polymer, a photoacid generator, and a solvent capableof dissolving both the electroconductive polymer and the photoacidgenerator; exposing portions of the organic active film to light ofsufficient energy and wavelength to activate the photoacid generator,removing exposed regions of the organic active film using a developersolution to obtain an organic active pattern; forming an upper electrodepattern on the organic active pattern whereby regions of the organicactive pattern are arranged between corresponding portions of the lowerelectrode pattern and the upper electrode pattern to form a plurality ofmemory cells; and providing circuitry configured for writing data to thememory cells and for reading data from the memory cells.
 9. The methodof forming an organic memory device according to claim 8, furthercomprising: providing a barrier layer on the lower electrode patternbefore depositing the photosensitive composition.
 10. The method offorming an organic memory device according to claim 9, wherein thebarrier layer comprises a material selected from a group consisting ofSiO_(x), AlO_(x), NbO_(x), TiO_(x), CrO_(x), VO_(x), TaO_(x), CuO_(x),MgO_(x), WO_(x), AlNO_(x), Alq3, polymethylmethacrylate, polystyrene,PET, and combination and mixtures thereof.